1. Field of the Invention
The present invention relates in general to dryers and more particularly to air dryers, such as the type of air dryers wherein articles are placed in a chamber and heated air is passed through the chamber, such as in a clothes dryer.
2. Description of the Prior Art
A typical air dryer for drying articles such as clothes, has an outer cabinet, a rotatable drum within the cabinet, a fan for drawing air in through the cabinet and passing it to the drum and a discharge duct for exhausting the air from the drum to the atmosphere. Usually, dryers of this type have one or more electrical heating elements located in the inlet air duct to heat the air before it passes to the drum. Alternatively, the heat is supplied from a source of gas. Conventionally, dryers of this type have a main on/off switch and an adjustable timer so that a user can select any one of a range of drying times. A heating control switch ultimately varies the amount of power supplied to the heating elements.
In order to control the temperature of the air flowing through the drum in the dryer a thermostat element is provided, typically in the discharge duct. A bias heater is physically located next to the thermostat element and supplies additional energy to the thermostat element depending upon the temperature setting which the user has selected for the dryer. The thermostat element breaks the high current to the heaters in the inlet duct when the thermostat is heated to a predetermined point which is determined by the temperature of the air in the discharge duct plus the energy supply from the bias heater. Thus, the more energy which is supplied to the bias heater, the lower the temperature of the air flowing through the drum and vice versa.
Modern dryers typically are microprocessor controlled and the number of actual controls which the user has access to is less than for older type dryers. Prior art control circuits for dryers using a microprocessor typically have involved complex circuitry often including analog to digital converters. The present invention provides a simpler solution to a control circuit in a microprocessor controlled dryer and especially without the use of analog to digital converters.